The role of LRF and gonadal steroids in the regulation of gonadotropin synthesis and release will be investigated in vitro, utilizing pure cultures of LH or FSH secreting cells. An attempt will be made to clarify the role of 3'5'-cyclic AMP in mediating the action of LRF and gonadal steroids and to explore the chemical nature of specific cell receptors for LRF and gonadal steroids. A study will be conducted to compare the ultrastructure of LH and FSH secreting cells and to determine what, if any, ultrastructural changes occur following various experimental treatments. Pure cultures, secreting either LH or FSH, will be initiated with single anterior pituitary cells, planted in individual microwells. The functional identity of the cultures will be determined by radioimmunoassay of the culture media for LH or FSH.